Restoration of insulin is critical for the treatment of insulin- dependent diabetes mellitus. Transplantation of pancreatic islet cells is a strategy for insulin replacement which has not worked well for unclear reasons. Recent work has demonstrated that pancreatic islet cells express receptors for extracellular ATP, termed P2 receptors. These receptors increase intracellular calcium which leads to a regenerative secretion of ATP, and subsequent coordination of calcium signals among cells. Thus stimulation of a calcium response in a single cell results in the propagation of a calcium rise in the whole cell population. These calcium signals are critical for proper insulin secretion, and possibly for regulating cell death. The studies in this proposal will define the expression and function of P2 receptors in rat and human islets and in several insulinoma cell lines. Furthermore, they will test the hypothesis that the regenerative signal propagated by P2Y receptors modulates the physiologically-important insulin secretion that is mediated by changes in the blood glucose concentration. These studies will employ a variety of molecular and biochemical techniques, and will also use fluorescence ratio imaging to study calcium responses in these cells. By understanding the way in which extracellular ATP and P2 receptors alter insulin secretion, these studies will determine whether this pathway is important in determining the insulin response to changes in the blood sugar level. These studies may therefore have important implications for islet cell transplantation strategies, and may offer new approaches to refining the techniques of islet cell transplantation. They may also identify new targets for the development of agents that would be useful in the treatment of diabetes because they will shed light on the basic mechanisms by which extracellular ATP alters islet function.